Folic Acid Generally
Folic acid is a vitamin. It plays a crucial role in DNA synthesis, and in hematopoiesis (although the details of this role remain undefined). Folic acid is involved, for example, in single carbon transfers (such as those required for purine and pyrimidine metabolism), and in the re-methylation of homocysteine to methionine.
Folic acid is available, primarily as the polyglutamate, from dietary sources such as whole grains, mushrooms, vegetables, red meat, fish and legumes. Supplementation, however, is provided in the form of the monoglutamate (pteroglutamic acid). Folic acid is absorbed primarily in the proximal small bowel, is highly protein-bound, and is stored in the liver. Almost no unchanged folic acid appears in the urine under normal circumstances, unless excess is provided.
Minimum requirements of folic acid are in the range of 50 .mu.g/day, and increase 3 to 6 times during pregnancy and/or lactation. The U.S. recommended daily allowance for pregnant women is 400 .mu.g/day, and the average pharmacological replacement dose is between 1 and 5 mg/day. Most prenatal vitamins contain 1 mg of folic acid.
The total body store of folic acid is about 5 mg. When a folic acid-deficient patient is treated, reversal of the deficiency begins rapidly (reticulocytosis within 4 days) and resolves within 2 months. If folic acid is administered at a rate of only 50 .mu.g day, assuming no dietary or other intake, signs of folic acid deficiency are manifest after an approximately 3 month lag time. In cases of increased bodily folic acid requirements, such as pregnancy or lactation, this time frame is shortened to 2 to 4 weeks. Fortunately, folic acid supplementation in otherwise healthy young women who have such increased folic acid needs is an accepted practice.
Folic acid has not been reported to cause adverse effects when administered in reasonable, pharmacological doses. The only reported adverse reaction for folic acid is a decreased level of plasma zinc in the case of prolonged high-dose administration.